Three types of chemosensors are being studied: I. The central CO2 and H ion chemoreceptor sites for the control of the tidal volume of respiration. II. The emetic chemoreceptor trigger zone in the area postrema of the medulla oblongata. III. The chemoreceptor locus in the nodose ganglion of the vagus nerve responsible for veratrum-induced vomiting. Our research plan encompasses the following approaches for each chemosensor. (1) Physiological and morphological characterization of the responding system. (2) Functional isolation of the receptive element. (3) Manipulation of the sensed environment. Experiments are performed on chronic unanesthetized cats and on acutely decerebrated cats. BIBLIOGRAPHIC REFERENCES: Borison, H.L., J.H. Hurst, L.E. McCarthy and R. Rosentein. Arterial hydrogen ion versus CO2 on rate and depth of breathing in decerebrate cats. Resp. Physiol., 1977 (in press). Costello, D.J. and H.L. Borison. Naloxone antagonizes narcotic self-blockage of emesis in the cat. J. Pharmacol: Exper. Therap., 1977 (in press).